Improved charge-control models of power bipolar transistors

This paper proposes two improved lumped circuit models for power bipolar junction transistors (BJT) which can predict the switching characteristics. Currently existing models in circuit simulators can achieve the delay time, rise time and the storage time performance in various switching topologies but fail to account for the decay of the excess stored charge in the drift region due to recombination. It is shown that the models that include the decay of the trapped charges due to recombination can exhibit current tail during hard-switching and soft switching turn-off (zero current switching and zero voltage switching) as seen in measured results. The results obtained from simulation are compared and validated with measured data. A closer prediction of switching losses and switching time of the device under various switching stresses and in various switching topologies is achieved with the use of these models.